Method for fabricating light emitting device

ABSTRACT

Provided is a method for fabricating a light emitting device. The method includes forming a gallium oxide layer; forming a first conductive type semiconductor layer, an active layer, and a second conductive type semiconductor layer on the gallium oxide layer; forming a non-conductive substrate on the second conductive type semiconductor layer; separating the gallium oxide layer forming a conductive substrate on the first conductive type semiconductor layer; and separating the non-conductive substrate.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.12/712,584 filed on Feb. 25, 2010 now U.S. Pat. No. 8,039,362 claimingthe benefit of Korean Patent Application No. 10-2009-0016020 filed Feb.25, 2009, both of which are hereby incorporated by reference for allpurpose as if fully set forth herein.

BACKGROUND

Embodiments relate to a method for fabricating a light emitting device.

Nitride semiconductors are attracting much attention for the fields ofoptical devices and high-power electronic devices because of their highthermal stability and wide band gap energy. In particular, blue lightemitting devices (LEDs), green LEDs, and UV LEDs that use nitridesemiconductors have been commercialized and are being widely used.

Nitride semiconductor LEDs commercialized in recent years include anitride semiconductor layer, which is organic-chemically deposited overa sapphire substrate that is a heterogeneous substrate. A galliumnitride (GaN) substrate having the same material as a nitridesemiconductor thin film is too expensive. Thus, it is difficult tocommercially utilize the GaN substrate. The sapphire substrate widelyused in recent years has an electrically insulating characteristic.Thus, a nitride semiconductor LED formed on the sapphire substrate has alateral type structure in which cathode and anode metal pads are formedin one direction of the substrate.

Generally, a lateral type LED structure has a limitation in which aportion of a light emitting layer should be etched to form a negativeelectrode. Also, since the electrodes are disposed on one side of thesubstrate, current is not uniformly injected into the light emittinglayer when the current is injected. Such un-uniform injection of thecurrent deteriorates electronic reliability and light emissionefficiency.

BRIEF SUMMARY

Embodiments provide a method for fabricating a light emitting device inwhich a nitride semiconductor thin film can be effectively separatedfrom a substrate

In one embodiment, a method for fabricating a light emitting device(LED) comprises: forming a gallium oxide layer; forming a firstconductive type semiconductor layer, an active layer, and a secondconductive type semiconductor layer on the gallium oxide layer; forminga second electrode layer on the second conductive type semiconductorlayer; and separating the gallium oxide layer.

In another embodiment, a method for fabricating a light emitting device(LED) comprises: forming a gallium oxide layer; forming a firstconductive type semiconductor layer, an active layer, and a secondconductive type semiconductor layer on the gallium oxide layer; forminga non-conductive substrate on the second conductive type semiconductorlayer; separating the gallium oxide layer forming a conductive substrateon the first conductive type semiconductor layer; and separating thenon-conductive substrate.

In further another embodiment, a method for fabricating a light emittingdevice (LED) comprises: forming a gallium oxide layer; forming a nitridesemiconductor layer on the gallium oxide layer; separating the galliumoxide layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a light emitting device (LED) according toa first embodiment.

FIGS. 2 to 5 are sectional views of a method for fabricating the LEDaccording to the first embodiment.

FIG. 6 is a sectional view of a light emitting device (LED) according toa second embodiment.

FIGS. 7 to 10 are sectional views of a method for fabricating the LEDaccording to the second embodiment.

FIGS. 11 to 12 are sectional views of a method for fabricating an LEDaccording to a third embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the descriptions of embodiments, it will be understood that when alayer (or film) is referred to as being ‘on’ another layer or substrate,it can be directly on another layer or substrate, or intervening layersmay also be present. Further, it will be understood that when a layer isreferred to as being ‘under’ another layer, it can be directly underanother layer, and one or more intervening layers may also be present.Also, it will be understood that when a layer is referred to as being‘on’ or ‘under’ another layer, the reference about ‘on’ and ‘under’ eachlayer will be made on the basis of drawings.

In the drawings, the thickness or size of each layer is exaggerated,omitted, or schematically illustrated for convenience in description andclarity. Also, the size of each element does not entirely reflect anactual size.

(First Embodiment)

FIG. 1 is a sectional view of a light emitting device (LED) according toa first embodiment.

A light emitting device (LED) according to a first embodiment mayinclude a second electrode layer 140, a second conductive typesemiconductor layer 130 disposed on the second electrode layer 140, anactive layer 120, and a first conductive semiconductor layer 110. Thefirst embodiment may include a roughness R disposed on the firstconductive type semiconductor layer 110, but is not limited thereto.

Gallium oxide (Ga2O3) has an energy band gap of about 4.8 eV. Also,gallium oxide is transparent and has superior conductivity. Electronssuch as aluminum (Al) and indium (In) may be mixed with gallium oxide toeasily adjust the band gap and physical and chemical properties ofgallium oxide. Gallium oxide has a monoclinic structure. Thus, it may bepossible to grow a superior nitride semiconductor thin film on a galliumoxide substrate.

In particular, gallium oxide having the monoclinic crystal structure hasa cleavage characteristic that is a proper characteristic of a materialwith respect to a (100) or (001) crystallographic plane. The cleavagecharacteristic represents a property in which a crystalline material issplit into pieces using a specific crystallographic plane as a boundary.In a crystal structure in which atoms are stacked in a certain rule,when a face-to-face coupling force between specific crystallographicatom planes is very weaker than that between other crystallographic atomplanes, the cleavage occurs along a corresponding crystal plane. Thecrystal cleavage may easily occur in any direction parallel to thecrystallographically same cleavage surface.

According to a method for fabricating the LED according to thisembodiment, since the thin film is separated using the proper cleavagecharacteristic of a crystal material of gallium oxide, a high-qualitynitride semiconductor thin film having economical, simplified, andmass-productive characteristics may be fabricated.

Also, the nitride semiconductor LED fabricated using a method forfabricating the LED according to this embodiment may be greatlycontributed in realization of a vertical type nitride semiconductor LEDhaving high power, high efficiency, and high reliability.

Hereinafter, a method for fabricating an LED according to the firstembodiment will be described with reference to FIGS. 2 to 5.

As shown in FIG. 2, a first substrate 100 is prepared. A substratehaving a crystallographical structure that may form a nitridesemiconductor (AlxInyGa1-x-yN (0≦x,y≦1)) thin film may be fundamentallyused as the first substrate 100. For example, the first substrate 100may be formed of sapphire, Si, and SiC, or gallium oxide (Ga2O3), GaN,and AlN, or other metal oxides, but is not limited thereto.

The preparing of the first substrate 100 may include cleaning a surfaceof the first substrate 100 using chemical wet cleaning or oxygen,nitrogen, or a mixed gas thereof at a high temperature.

A gallium oxide layer 105 using a (100) or (001) crystallographic planehaving a cleavage characteristic as a growth surface is formed on thefirst substrate 100. A thin film of the gallium oxide layer 105 may bedeposited using a thin film deposition method. For example, chemicalvapor deposition or sputtering may be used as the thin film depositionmethod.

In case of a gallium oxide single crystal substrate in which a surfacethereof has a crystallographic cleavage characteristic such as the (100)or (001) crystallographic plane, the thin film of the gallium oxidelayer 105 may not be deposited.

A gallium metal may be deposited on the first substrate 100, and thenthermally oxidized at a high temperature to form the thin film of thegallium oxide layer 105. The gallium oxide thin film disposed on thefirst substrate 100 may be thermally treated at a high temperature underan oxygen atmosphere to improve crystal quality. The gallium oxide layer105 is formed based on Ga2O3. Also, the gallium oxide layer 105 may beformed of a mixture or compound in which Al and In, or other elementsare mixed with each other within a range in which the crystallographiccleavage characteristic is maintained.

A nitride semiconductor layer including a first conductive typesemiconductor layer 110, an active layer 120, and a second conductivetype semiconductor layer 130 is formed on the gallium oxide layer 105.

The first conductive type semiconductor layer 110 can be a N-typesemiconductor layer or a P-type semiconductor layer. Also, the secondconductive type semiconductor layer 130 can be a P-type semiconductorlayer or a N-type semiconductor layer. A second semiconductor layer offirst conductive type 110 can be formed on the conductive typesemiconductor layer 130, and thereby the light emitting structure can bea NPN type or PNP type.

The forming of the nitride semiconductor layer on the gallium oxidelayer 105 or a gallium oxide substrate may further include performing anitridation process on a surface of the gallium oxide layer 105 at ahigh temperature using an ammonia gas. When the nitridation process isperformed, the ammonia gas supplying nitrogen atoms may be provided as amixed gas mixed with a carrier gas such as hydrogen, nitrogen, oroxygen.

The high-temperature nitridation process may be performed to form agallium oxynitride layer (not shown) on a surface of the gallium oxidelayer 105. The gallium oxynitride layer may serve as a buffer layer of anitride semiconductor layer to be grown later, and makes it possible toform a high-quality nitride semiconductor layer on the gallium oxidelayer 105. At this time, the electrical conductivity of the galliumoxynitride layer can be improved by supplying a silicon-containing gassuch as silane gas to the gas injected into the chamber.

Thereafter, a first conductive type semiconductor layer 110 is formed onthe gallium oxide layer 105. For example, the first conductive typesemiconductor layer 110 may be formed using a chemical vapor deposition(CVD) process, a molecular beam epitaxy (MBE) process, a sputteringprocess, or a hydride vapor phase epitaxial (HVPE) deposition process.Also, silane gas (SiH4) containing N-type impurities such astrimethylgallium gas (TMGa), ammonia gas (NH3), nitrogen gas (N2),hydrogen gas (H2), and silicon (Si) may be injected into a chamber toform the first conductive type semiconductor layer 110.

The first conductive type semiconductor layer 110 may be formed of oneor more of GaN, InN, AlN, InGaN, AlGaN, InAlGaN, AlInN, AlGaAs,AlInGaAs, GaP, AlGaP, InGaP, AlInGaP, and InP.

An active layer 120 is formed on the first conductive type semiconductorlayer 110. The active layer 120 severs as a layer in which electronsinjected through the first conductive type semiconductor layer 110recombine with electron holes injected through a second conductive typesemiconductor layer 130 to emit light having an energy determined by aproper energy band of an active layer (light emitting layer) material.

The active layer 120 may have at least one structure of a singlequantum-well structure, a multi quantum-well structure, a quantum-wirestructure, and a quantum dot structure. For example, in the active layer120, trimethyl gallium (TMGa) gas, ammonia (NH3) gas, nitrogen (N2) gas,and trimethyl indium (TMIn) gas are injected to form the multi-quantumwell structure, but is not limited thereto.

The active layer 120 may have one or more structures of an InGaN/GaNstructure, an InGaN/InGaN structure, an AlGaN/GaN structure, anInAlGaN/GaN structure, a GaAs/AlGaAs(InGaAs) structure, and aGaP/AlGaP(InGaP) structure.

Thereafter, a second conductive type semiconductor layer 130 is formedon the active layer 120. For example, bis(ethylcyclopentadienyl)magnesium (EtCp2Mg){Mg(C2H5C5H4)2} containing p-type impurities such astrimethyl gallium (TMGa) gas, ammonia (NH3) gas, nitrogen (N2) gas, andmagnesium (Mg) may be injected into the chamber to form a p-type GaNlayer of the second conductive type semiconductor layer 130, but is notlimited thereto.

A second electrode layer 140 may be formed on the second conductive typesemiconductor layer 130.

The second electrode layer 140 may include an ohmic layer 142, areflective layer (not shown), an adhesive layer (not shown), and asecond substrate 144. The second electrode layer 140 may be formed of atleast one of titanium (Ti), chrome (Cr), nickel (Ni), aluminum (Al),platinum (Pt), gold (Au), and tungsten (W).

For example, the second electrode layer 140 may include the ohmic layer142. At this time, a single metal or a metal alloy may be multi-stackedto improve the efficiency of electron hole injection. The ohmic layer142 may be formed of at least one of ITO, IZO(In—ZnO), GZO(Ga—ZnO),AZO(Al—ZnO), AGZO(Al—Ga ZnO), IGZO(In—Ga ZnO), IrOx, RuOx, RuOx/ITO,Ni/IrOx/Au, Ni/IrOx/Au/ITO, Ni, Pt, Cr, Ti, and Ag, but is not limitedthereto.

Also, the second electrode layer 140 may include a reflective layer (notshown) or an adhesion layer (not shown). For example, the secondelectrode layer 140 may include a metal layer containing Al, Ag, or analloy containing Al or Ag. The material such as Al or Ag may effectivelyreflect light generated at the active layer to improve light extractionefficiency of the LED. Also, for example, when the second electrodelayer 140 includes an adhesive layer, the reflective layer may serve asthe adhesive layer, or the adhesive layer may be formed using Ni or Au.

The second electrode layer 140 may include a second substrate 144. Thesecond substrate 144 may be formed of a metal having good conductiveproperties, a metal alloy, or a conductive semiconductor material toefficiently inject carriers. For example, the second substrate 144 maybe formed of one of more of copper (Cu), a Cu alloy, Si, molybdenum(Mo), SiGe, Ge, GaN, and SiC. The second substrate 144 may be formedusing an electrochemical metal deposition method or a bonding methodusing eutectic metals.

As shown in FIG. 3, a temperature of a sample increases to about 200° C.to about 900° C. using a rapid thermal processing equipment, and then,the sample is quickly cooled again. The cooling speed may be over about50° C. per at least minute. The gallium oxide layer 105 may have athermal expansion coefficient of about 8.2×10−6/° C./° C. to about8.5×10−6/° C., and a gallium nitride material may have a thermalexpansion coefficient of about 5.7×10−6/° C. Thus, the rapid thermalprocess causes a stress on an interface between the gallium oxide layer105 and the first conductive type semiconductor layer 110 that is anitride semiconductor due to a thermal expansion coefficient differencebetween the materials. Such the stress causes thin film separation alonga cleavage plane of the gallium oxide layer 105 disposed on theinterface.

When the thermal treatment temperature is greater than about 900° C.,the nitride semiconductor thin film may be deformed in quality, and thesecond electrode layer 140 may be collapsed. When the thermal treatmenttemperature is less than about 200° C., the stress is very small, andthus, it may be difficult to effectively cause the thin film separation.When the first substrate 100 is separated using the above-describedmethod, the first conductive type semiconductor layer 110 that is anelectron transport layer nitride semiconductor thin film is exposed.

As shown in FIG. 4, a wet etching process may be performed on theexposed first conductive type semiconductor layer 110 using a patternmask as an etch mask to form a surface roughness R. Since the firstconductive type semiconductor layer 110 is polarized by nitrogen, thewet etching process may be performed to form the roughness R on asurface of the first conductive type semiconductor layer 110. Theroughness R may effectively improve light extraction performance of theLED.

As shown in FIG. 5, the pattern mask 310 is removed. A first electrode150 may be formed on the exposed first conductive type semiconductorlayer 110 to fabricate the LED. At this time, the surface of the exposedfirst conductive type semiconductor layer 110 is wet-etched to form thefirst electrode 150. Since the gallium oxide material remaining on thesurface of the exposed first conductive type semiconductor layer 110 mayreduce an ohmic characteristic, an acid cleaning process may beperformed to remove the remaining gallium oxide material.

According to the method for fabricating the LED according to thisembodiment, a method for effectively separating the nitridesemiconductor thin film from the substrate is provided.

Also, according to the method for fabricating the LED according to thisembodiment, since the thin film is separated using the proper cleavagecharacteristic of a crystal material of gallium oxide, a high-qualitynitride semiconductor thin film having economical, simplified, andmass-productive characteristics may be fabricated.

Also, the nitride semiconductor LED fabricated using the method forfabricating the LED according to this embodiment may be greatlycontributed in realization of a vertical type nitride semiconductor LEDhaving high power, high efficiency, and high reliability.

(Second Embodiment)

FIG. 6 is a sectional view of a light emitting device (LED) according toa second embodiment.

In an LED according to a second embodiment, a first conductive typesemiconductor layer 110, an active layer 120, and a second conductivetype semiconductor layer 130 may be disposed on a conductive substrate200. Non-described numerals will be described in the followingfabrication method.

The second embodiment may adopt the technical features of the firstembodiment.

A method for fabricating an LED according to second embodiment will bedescribed with reference to FIGS. 7 to 10.

Like the first embodiment and FIG. 7, a gallium oxide layer 105 isformed on a first substrate 100. A first conductive type semiconductorlayer 110, an active layer 120, and a second conductive typesemiconductor layer 130 are formed on the gallium oxide layer 105.

Thereafter, a non-conductive substrate 210 is formed on the secondconductive type semiconductor layer 130. For example, the non-conductivesubstrate 210 that is a temporary support substrate is attached to thesecond conductive type semiconductor layer 130 that is a hole injectionlayer. A sapphire substrate may be used as the temporary supportsubstrate. The non-conductive substrate 210 that is the temporarysupport substrate may be physically fixed using a fixing pin or fixedusing a polymer adhesive material.

As shown in FIG. 8, a temperature of a sample increases to about 200° C.to about 900° C. using a rapid thermal processing equipment, and then,the sample is quickly cooled again. The rapid thermal process causes astress on an interface between the gallium oxide layer 105 and the firstconductive type semiconductor layer 110 that is a nitride semiconductordue to a thermal expansion coefficient difference between the materials.Such the stress causes thin film separation along to (100) or (001)plane of the gallium oxide layer 105 disposed on the interface. As aresult, the gallium oxide layer 105 may be separated, and the firstconductive type semiconductor layer may be exposed.

As shown in FIG. 9, a first electrode layer 115 may be formed on theexposed first conductive type semiconductor layer 110. The firstelectrode layer 115 may include an ohmic layer, a reflective layer, andan adhesive layer.

A conductive substrate 200 is formed on the first conductive typesemiconductor layer 110 or the first electrode layer 115. The conductivesubstrate 200 may be formed of a metal having thermally goodconductivity or a semiconductor material. When the conductive substrate200 is formed, a eutectic metal for bonding may be used.

As shown in FIG. 10, the non-conductive substrate 210 that is thetemporary support substrate may be removed to form a second electrode270 on the second conductive type semiconductor layer 130.

(Third Embodiment)

FIGS. 11 to 12 are sectional views of a method for fabricating an LEDaccording to a third embodiment.

The third embodiment relates to a method for separating a nitridesemiconductor layer 125 from a gallium oxide layer 105 when the nitridesemiconductor layer 125 is formed on the gallium oxide layer 105 in asingle layer. For example, the nitride semiconductor layer 125 may be aGaN semiconductor layer, but is not limited thereto.

For example, as shown in FIG. 11, the nitride semiconductor layer 125may be formed on the gallium oxide layer 105 as a thicker electrontransport single layer having a thickness of about 70 μm. The nitridesemiconductor layer 125 may be deposited using a chemical vapordeposition method or a hydride vapor phase epitaxy method.

According to the third embodiment, when the nitride semiconductor layer125 is formed as a thicker single layer, the nitride semiconductor layer125 may be separated through the following processes.

For example, as shown in FIG. 12, a thin film of the nitridesemiconductor layer 125 is grown within a thin film growth equipment.Thereafter, when the thin film growth equipment is cooled, the thin filmgrowth equipment is quickly cooled to self-separate the nitridesemiconductor layer 125 from the gallium oxide layer 105.

The gallium oxide layer 105 may have a thermal expansion coefficient ofabout 8.2×10−6/° C./° C. to about 8.5×10−6/° C., and a gallium nitridematerial may have a thermal expansion coefficient of about 5.7×10−6/° C.Thus, when the thin film growth equipment is quickly cooled after thethin film is grown, a stress occurs on an interface between the galliumoxide layer 105 and the nitride semiconductor layer 125 due to a thermalexpansion coefficient difference between the materials. Such the stresscauses thin film separation along a cleavage plane of the gallium oxidelayer 105 disposed on the interface.

At this time, the nitride semiconductor layer 125 may have a thicknessof at least about 70 μm. When the nitride semiconductor layer 125 doesnot have a sufficiently thicker thickness, the thin film may beself-separated. As a result, the thin film may not be maintained in itsoriginal shape and broken. The cooling speed may be over about 50° C.per at least minute. The separated nitride semiconductor layer 125 mayhave electrical conductivity, and be uses as a substrate of the LED.

The LED according to an embodiment may be applicable to a lightingsystem. The lighting system may include a lighting unit and a backlightunit. In addition, the lighting system may be applicable to trafficlights, a vehicle headlight, and a sign.

Any reference in this specification to “one embodiment,” “anembodiment”, “example embodiment”, etc., means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment of the invention. Theappearances of such phrases in various places in the specification arenot necessarily all referring to the same embodiment. Further, when aparticular feature, structure, or characteristic is described inconnection with any embodiment, it is submitted that it is within thepurview of one skilled in the art to effect such feature, structure, orcharacteristic in connection with other ones of the embodiments.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the spirit and scope of the principles ofthis disclosure. More particularly, various variations and modificationsare possible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

1. A method for fabricating a light emitting device (LED), the methodcomprising: forming a gallium oxide layer; forming a light emittingstructure on the gallium oxide layer, wherein the light emittingstructure comprises a first conductive type semiconductor layer, anactive layer, and a second conductive type semiconductor layer; forminga non-conductive substrate on the light emitting structure; separatingthe gallium oxide layer from the light emitting structure after formingnon-conductive substrate; forming a conductive substrate on the lightemitting structure; and separating the non-conductive substrate from thelight emitting structure after forming the conductive substrate.
 2. Themethod of claim 1, wherein the separating of the gallium oxide layercomprises: heating the gallium oxide layer at a temperature of about200° C. to about 900° C.; and quickly cooling the gallium oxide layer.3. The method of claim 1, wherein, in the separating of the galliumoxide layer, the first conductive type semiconductor layer comprises afirst conductive type GaN semiconductor layer, and the gallium oxidelayer is separated by an interface stress due to a thermal expansioncoefficient difference between the gallium oxide layer and the firstconductive type GaN semiconductor layer.
 4. The method of claim 3,wherein, in the separating of the gallium oxide layer, the gallium oxidelayer has a thermal expansion coefficient of about 8.2×10⁻⁶/° C./° C. toabout 8.5×10⁻⁶/° C., and the first conductive type GaN semiconductorlayer has a thermal expansion coefficient of about 5.7×10⁻⁶/° C.
 5. Themethod of claim 1, wherein, in the separating of the gallium oxidelayer, the gallium oxide layer is cleaved along a (100) or (001) plane.6. The method of claim 1, further comprising: performing a nitridationprocess on a surface of the gallium oxide layer before forming the lightemitting structure.
 7. The method of claim 6, wherein the nitridationprocess includes supplying a silicon-containing gas to a carrier gas.